OMEGA: Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité

OMEGA is a VIS/NIR hyperspectral imager. It acquires images of the surface and atmosphere of Mars with a footprint ranging from 300 m to 5 km depending on the altitude of the spacecraft. On each pixel, it provides the spectrum in 352 spectral channels covering the range 0.35-5.1 μn. In this domain, most surface (minerals, frost, ice) and atmospheric (gas, aerosols, clouds) constituents have diagnostic features that enable their identification. Consequently, OMEGA can monitor their time and space dependence. As a major outcome, OMEGA can derive the evolution of Mars over all timescales, from geological and climatic to seasonal variations. This chapter presents the main results obtained after four years of operation. The results are discussed in the framework of Mars history that they are likely to modify profoundly, in particular with regard to the role of water. A very early era of potential habitats has been identified, with the relevant terrains located and the environmental conditions deciphered. It is suggested that this era was followed by a period of global climatic change, towards a cold and dry environment that has lasted to the present day.